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The Surprising Ecology of Dust (1)

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High in the snowfields atop the Rocky Mountains in Colorado, things are not as pristine as they used to be. Dust from the desert Southwest is sailing into the Rockies in increasing quantities and settling onto the snow that covers the peaks, often streaking the white surface with shades of red and brown.

The amount of dust that settles on snow varies from year to year. From 2005 to 2008, about five times as much dust fell on the Rockies as during the 1800s, and those years are characterized by researchers as moderately dusty. In 2009 and 2010, however, the Rockies saw an extreme dust scenario, with the amount of dust blowing onto the mountains mushrooming to five times more than those moderate years. The cause, scientists say, was increasing drought — linked to a warming climate — and human development.

Because darker, dust-flecked snow absorbs more solar energy and warms faster than pure white snow, it means snow cover melts earlier — a lot earlier. “It’s not subtle at all,” said Jeff Deems (research scientist with the National Snow and Ice Data Center in Boulder, Colorado). “There is 30 to 60 days difference in the melt out. Over a larger watershed, it’s massive.”

With the snow disappearing earlier and the growing season significantly extended, plants consume more water and transpire it into the atmosphere. That is water that would otherwise go into streams but is now lost, and Deems says: “This translates into 5% less water flowing into the Colorado River in dusty years, a significant amount”. The more rapid rate of snowmelt also has a cascade of effects, with the darker, bare ground absorbing more heat and warming the atmosphere.

The same phenomenon is happening in other mountain ranges across the globe, most notably the Himalayas and the Caucasus Mountains, where grazing, desertification, and development are taking place upwind of glaciers and snow-covered terrain, increasing the deposition of dust on those surfaces. As farming and other development spreads into arid regions, vegetation is destroyed, exposing the soil to wind erosion.

The major impacts of a warming climate are well known: hotter temperatures, more — and more intense — storms, melting glaciers and sea ice, drier climates in many regions and wetter weather in others. But some researchers say one major element of climate change is being overlooked: dust. Dust plays a fundamental role in the world’s ecological processes, and the dynamics of dust are changing as the climate changes.  

Although the issue is poorly studied, it’s clear that dust dynamics are shifting in two main ways. Humans are the main cause of an increasing amount of dust in the atmosphere. As farming, grazing, and other development in places such as the Horn of Africa or the U.S. Southwest spread deeper into arid regions, vegetation is destroyed, exposing the soil to wind erosion. In addition, increasing drought due to a warming climate is a major cause of the dust problem, as it kills vegetation and uncaps the soil, allowing it to become windborne.

This has both positive and negative effects. More dust, for example, means more nutrients and minerals, such as iron, are being transported long distances, which stimulates the growth of oceanic plankton — an essential link in the marine food chain. But increasing quantities of dust could cause serious problems for parts of the world, from decreased water flow in some mountain regions to increased human exposure to dust-borne pathogens, a growing health concern.

Dust covers the snow in the San Juan Mountains in Colorado during an extreme dust year in 2009. Chris Landry/Center for Snow and Avalanche Studies

In the United States, the 2017 National Climate Assessment found that warmer temperatures are reducing soil moisture in parts of the West, and also predicts more drought in the coming years. These factors kill vegetation that keeps soil in place and have already led to more dust storms. And winds that blow in from the Pacific Ocean are increasing as ocean temperatures heat up. That, in turn, draws in drier north winds that suck moisture out of the soil in the southwestern U.S. The frequency of dust storms there has more than doubled since the 1990s — from 20 per year to 48 in the 2000s — and will likely continue to increase, according to one study.

Source: ENN, 30-11-2017,

From: Yale Environment 360
November  2017